The Fischer-Tropsch process discovered the last century and immediately used in industry occurs under high pressure and in the presence of catalysts based on metals of group VIII of the Mendeleev's periodic table. The process is exothermic.
The main requirements for the process, particularly for the arrangement of a catalyst bed for the Fischer-Tropsch process, include high concentration of the catalytically-active component in the reaction volume, small typical size of the catalyst active particles, high effective thermal conductivity of the catalyst bed, developed gas-liquid interface, provision of a convective gas flow regime that should be close to a plug flow regime, and these requirements define a close relationship between the choice of the catalyst and reactor design.
It is known that heterogeneous exothermic processes can be technologically implemented in a fluidized-bed reactor, or in a liquid phase with a suspended catalyst aka slurry-phase bed, or in a fixed bed reactor.
At present, fixed bed reactors are most widely used in the area of catalytic technologies due to simplicity and ripeness of their mechanical design. Such reactors comprise reaction tubes, which in turn contain a heterogeneous system comprising at least two phases, i.e. solid particles of a catalyst and a reaction mixture in the form of gas and/or liquid, which moves among the above-said solid particles. The solid particles of catalyst usually exist as pellets or granules. Both chemical transformations on the catalyst surface and physical processes such as heat- and mass-transfer of reactants and products in the bed take place simultaneously in the reactor.
One of main problems faced by a skilled in the art when developing catalytic tubular reactors for the Fischer-Tropsch synthesis is ensuring high selectivity of the process to the sum of liquid products, and especially selectivity to the most important C10-C18 fraction that is the basis of diesel and kerosene fuels.
A method for solving this problem is known and described in public literature:    P. M. Maitlis, A. deKlerk (eds.). Greener Fischer-Tropsch Processes. Wiley-VCH, Weinheim, 2013. P. 372;    Steynberg A. P., Dry M. E. Fischer-Tropsch Technology.—Elsevier, 2004. V. 64. 722 p.;    J. T. Bartis, F. Camm, D. S. Ortiz. Producing Liquid Fuels from Coal: Prospects and Policy Issues. RAND Corporation, 2008. P. 167;    A. deKlerk, E. Furimsky. Catalysis in the Refining of Fischer-Tropsch Syncrude. RSC Publishing, Cambridge, UK, 2010. P. 279;    U.S. Pat. No. 7,157,501 (2006).
According to this known method, cobalt Fischer-Tropsch synthesis catalysts are used. These catalysts provide occurring the Fischer-Tropsch synthesis at Anderson-Schulz-Flory factor not less than 0.88 are used. Such catalysts allow to obtain a sum of liquid products with high selectivity, over 80%, however, heavy waxes are the main product, whereas the content of C10-C20 fraction is less than 40%. In order to compensate for this disadvantage, a hydrocracking reactor is additionally used to ensure wax conversion into lighter hydrocarbons in the presence of hydrogen and by means of a special catalyst.
Another method for solving this problem, which includes combined use of a mixture of granules of a Fischer-Tropsch synthesis catalyst and zeolite granules, is described in the following information sources:    Z.-W. Liu, X. Li, K. Asami, K. Fujimoto. Catal. Today, 104, 41 (2005);    Z.-W. Liu, X. Li, K. Asami, K. Fujimoto. Energy Fuels, 19, 1790 (2005);    T.-Sh. Zhao, J. Chang, Y. Yoneyama, N. Tsubaki. Ind. Eng. Chem. Res., 44, 769 (2005);    A. Freitez, K. Pabst, B. Kraushaar-Czarnetzki, G. Schaub. Ind. Eng. Chem. Rev., 50, 13732 (2011);    US Patent Application No. 2006223893 A1 (2006);    EP Patent No. 1558701 A1 (2003).
Also known are technical solutions using sequential arrangement of a layer of a zeolite-containing catalyst or another catalyst active in hydrocarbon hydrotransformations after a layer of a Fischer-Tropsch synthesis catalyst:    Z.-W. Liu, X. Li, K. Asami, K. Fujimoto. Appl. Catal. A: Gen., 300, 162 (2006);    A. M. Subiranas, G. Schaub. Int. J. Chem. React. Eng., 5, A 78 (2007);    U.S. Pat. No. 7,973,086 B1 (2010);    U.S. Pat. No. 8,519,011 B2 (2013);    KR Patent No. 20100071684 A (2008);    I. Nam. K. M. Cho, J. G. Seo, S. wan Hwang, K.-W. Jun, I. K. Song. Catal. Lett., 130, 192-197 (2009);    US Patent Application No. 2009143220 A1 (2008);    Patent Application WO 2011/090554 (2009);
or granules of a Fischer-Tropsch synthesis catalyst are used in zeolite capsules:    S. Sartipi, J. E. van Dijk, J. Gascon, F. Kaptejn. Appl. Catal. A: Gen., 456, 11 (2013);    G. Yang, Ch. Xing, W. Hirohama, Y. Jin, Ch. Zeng, Y. Suehiro, T. Wang, Y. Yoneyama, N. Tsubaki. Catal. Today, 215, 29 (2013);    Yu. Jin, R. Yang, Y. Mori, J. Sun, A. Taguchi, Y. Yoneyama, T. Abe, N. Tsubaki. Appl. Catal. A: Gen., 456, 75 (2013).
The zeolite property to serve as a hydrocracking catalyst and convert resulting waxes into lighter hydrocarbons in situ is used in the above-mentioned known methods using zeolite. Therefore, these methods are often referred to as the use of bifunctional catalysts or the use of hybrid catalysts or the use of bifunctional (hybrid) bed. These methods provide minimum wax content in the product and one-pass formation of light hydrocarbon mixture in a simple, inexpensive reactor. However, these methods are characterized by a low conversion rate of CO and H2 as well as by low yield of the C10-C20 fraction.
Known in the art is a vertical reactor with a cascade of three sequential fixed catalyst layers for carrying out the Fischer-Tropsch synthesis in the first layer, oligomerization in the second layer and hydrocracking/isomerization in the third layer to obtain middle distillates (Sihe Zhang, Rui Xu, Ed Durham and Christopher B. Roberts. AlChE Journal. V. 60, Issue 7, pp. 2573-2583).
It has been demonstrated that the Fischer-Tropsch synthesis using a multilayer fixed bed leads to decrease of selectivity in the formation of olefins and C26+ hydrocarbons as well as notable increase of the yield of branched paraffins and aromatic compounds. The use of supercritical hexane as a reaction medium results in considerable decrease of selectivity in the formation of CH4 and CO2. Besides, significant quantities of aldehydes and cycloparaffins are formed in supercritical conditions. In this reactor, a co-precipitated iron-zinc based catalyst promoted by copper and potassium is used as a Fischer-Tropsch synthesis catalyst, amorphous aluminosilicate is used as a catalyst for the oligomerization reaction, and palladium applied on amorphous aluminosilicate is used as a hydrocracking/isomerization catalyst. The reactor is provided with three heating zones. The temperature of 240° C. is maintained in the upper layer for occurring the Fischer-Tropsch synthesis whereas 200° C. is maintained in the middle layer for the oligomerization reaction and 330° C. is maintained in the lower layer. Hexane is added at the rate of 1 ml/min. The pressure of 76 bars is maintained in the reactor. H2:CO ratio is 1.75. As a result of the syngas passing through the three catalyst layers of the multilayer fixed bed, a mixture of hydrocarbons is formed during CO conversion. The mixture comprises 43 wt % of C12-C22 and 10 wt % of C22+. Disadvantages of this known device are supercritical conditions requiring high energy consumption to create the pressure of 76 bars, high selectivity in CO2 formation (13%), low yield of the target product and high content of waxes.
Known in the art is a porous catalyst comprising palladium on mesoporous aluminium oxide for the Fischer-Tropsch hybrid synthesis. The catalyst is to be used in a continuous device to carry out a dual reaction for the purpose of obtaining C10-C20 middle distillate (KR Patent 20100071684 A, IPC B0021/04, B0023/44, B01J35/04, B01J37/04, 2008). The device is a dual-chamber reactor. A Co/TiO2 Fischer-Tropsch synthesis catalyst is introduced into the upper chamber. The synthesis occurs at 200-400° C., 5 to 30 bars, syngas flow rate of 100 to 1,000 ml/gcat·h−1 and H2:CO ratio of 1.5. In the second, downstream chamber, a Pd/Al2O3 catalyst layer is located. The temperature of 270-350° C. is maintained in this layer. Furthermore, hydrogen is additionally introduced between the chambers. Said reaction results in the formation of hydrocarbon mixtures comprising 30-50 wt % of C1-C9 hydrocarbons, 45-55 wt % of C10-C20 hydrocarbons and 5-15 wt % of C21+ hydrocarbons. A disadvantage of this known solution is complexity of the Fischer-Tropsch hybrid synthesis device that includes two chambers operated at different temperatures, whereas additional quantity of hydrogen needs to be introduced into the second chamber. Other disadvantages are the use of expensive palladium, complicated production of mesoporous aluminium and the yield of target C10-C20 hydrocarbons of less than 55%.
Known in the art is a method for syngas conversion in a mixture of liquid hydrocarbons used in fuel and petroleum production (U.S. Pat. No. 8,519,011 B2, IPC C07C27/00, 2013). The syngas is brought into contact with at least two layers of a syngas conversion (Fischer-Tropsch synthesis) catalyst and with a subsequent layer of a mixture of hydrocracking and hydroisomerization catalysts or subsequent separate layers of hydrocracking and hydroisomerization catalysts. This process may be carried out within a single reactor at common temperature and common pressure in the reactor. The process ensures high yield of liquid hydrocarbons in the range of C5-C12 naphtha (40-80 wt %) and low yield of waxes (less than 5%). A catalyst comprising 20% of Co, 0.5% of Ru and 3% of Zr/SiO2 is used as the syngas conversion catalyst. Pt/H-zeolite is used as the hydrocracking catalyst and Pd/H-zeolite is used as the hydroisomerization catalyst. Disadvantages of this method are use of expensive metals in the composition of the hydrocracking and hydroisomerization catalysts and low syngas conversion rate per pass, which compels to use of recycling that makes the process notably more expensive.
The closest prior art is a process for converting syngas to a hydrocarbon mixture, which includes contacting a feed comprising a mixture of carbon monoxide and hydrogen with at least two layers of a syngas conversion catalyst comprising a metal component, and at least two layers of a hydrocracking catalyst comprising an acidic component, in an alternating arrangement of layers within a single reaction tube, such that the feed sequentially contacts with at least a first layer of the syngas conversion catalyst, a first layer of the hydrocracking catalyst, a second layer of the syngas conversion catalyst and a second layer of the hydrocracking catalyst, thereby resulting in a hydrocarbon mixture which at ambient conditions contains 0-20 wt % of CH4, 0-20 wt % of C2-C4, greater than 70 wt % of C5+, 40-80 wt % of C5-C12 and 0-5 wt % of C21+ n-paraffins (U.S. Pat. No. 7,973,086 B1, IPC C07C27/00, 2011). The size of syngas conversion catalyst particles is 1 to 5 mm and the weight ratio of the active components of the hydrocracking catalyst to the syngas conversion catalyst is 2:1 to 100:1. The weight ratio of the acidic component in the hydrocracking catalyst to the metal component in the syngas conversion catalyst is 0.1:1 to 100:1. The synthesis occurs at 3-30 atm and 160-300° C. The obtained liquid hydrocarbons (naphtha) do not contain waxes and have a cloud point temperature of 15° C. Disadvantages of this known solution are use of expensive metals in the composition of the hydrocracking catalysts and low syngas conversion rate per pass, which compels to use recycling that makes the process notably more expensive.